Development of a Foot-Care Cream Containing Kaffir Lime Oil for Foot Self-Massage: A Randomized Active-Controlled Trial in Older Adults with Type 2 Diabetes

Background/Objectives: Diabetic peripheral neuropathy (DPN) causes foot numbness, pain, and dry skin in older adults with type 2 diabetes (T2D). We developed a Kaffir lime oil foot cream and evaluated its effectiveness and acceptability for self-massage. Methods: Oil composition was analyzed by GC-MS, and anti-inflammatory activity was tested in vitro in LPS-stimulated RAW264.7 macrophages. The cream was tested for stability and microbiological quality. In a randomized active-controlled trial, 92 older adults with T2D and foot numbness were matched and randomized to self-massage with 0.6% Kaffir lime oil cream or 0.5% methyl salicylate cream, twice daily, three days/week, for eight weeks. Primary outcomes were foot numbness and neuropathic pain (DN4, scored per foot and averaged); skin moisture and foot-care behavior were secondary. Outcomes were analyzed with mixed-design ANOVA and ANCOVA. Results: The oil (mainly limonene and β-pinene) reduced nitric oxide production in vitro (IC50 = 224.21 µg/mL). Outcomes improved over time in both groups (all p < 0.01). Numbness showed a group-by-time interaction (p = 0.043), but no between-group difference in numbness was significant at any time point. At week 8, DN4 was slightly lower in the experimental group (adjusted difference −0.43 points on a 0–10 scale; Bonferroni-adjusted p = 0.030), without a significant group-by-time interaction (p = 0.163). No visible skin reactions were observed, and satisfaction among a random subsample of 15 experimental-group participants was high (4.67/5). Conclusions: The cream was acceptable and was associated with slightly lower DN4 scores at week 8; other outcomes did not differ significantly between groups. The numbness and DN4 findings are exploratory and require confirmation in larger, longer, blinded trials in patients with painful DPN. Trial registration: Thai Clinical Trials Registry, TCTR20261007025. Registered retrospectively (first submitted 3 October 2026).